A conventional electromagnetic valve used for flow controlling or pressure controlling includes a valve body having an inlet port, an outlet port and a drain port. A spool is fitted in the valve body in a slidable manner and is adapted to be operated in such a manner that the spool is in a counter balanced state by being applied with an output force of a linear solenoid and the urging force of a spring, the hydraulic pressure at the output port, or the sum of the hydraulic pressure at the output port and the urging force of the spring. An electromagnetic valve of this type is disclosed in Japanese Patent Laid-Open Publication No. Hei.7-301346 published without examination in 1995.
With this type of electromagnetic valve, to obtain the designed performance of the valve, smooth movements of the spool and a plunger from which the output force of the linear solenoid is derived are necessary and are established subject to coaxial alignment between the spool and the plunger. To realize this coaxial alignment in the known electromagnetic valve, an alignment engaging portion is provided between a casing of the linear solenoid and the valve body.
However, with this construction, a higher dimensional precision is required for the casing and the related parts or elements by which the plunger is aligned with the casing. This need for precision makes it difficult to reduce the production costs associated with known electromagnetic valve constructions.
In addition, to avoid direct engagement of the plunger with a yoke when electric current flowing through the coil of the linear solenoid reaches its maximum value, a stopper member formed from non-magnetic material is provided between the plunger and yoke. This also contributes to making it difficult to reduce the production cost associated with the known electromagnetic valve constructions.
In light of the foregoing, a need exists for a spool valve type electromagnetic valve which is not as susceptible to the aforementioned disadvantages and drawbacks.
It would thus be desirable to provide a spool valve type electromagnetic valve having a coaxially aligned spool and plunger that is capable of being manufactured at a lower cost.